Pressure but not the fraction of oxygen is altered in the aircraft cabin

With great interest we have read the paper of Catherine R Epstein and colleagues ¹ and we do appreciate research activity for in-flight medical events or emergencies. It is important to analyse causes, consequences and treatment options for this specific scenario to improve passenger safety. We agree that the content of emergency medical kits varies significantly; ² we feel that emergency medical kits should be harmonized throughout the industry.

Besides, we may stress one aspect of the introduction. During flight, cabin altitude is approximately 6000–8000 ft, as stated in the paper. However, the reason is not a lower fraction of oxygen ¹ —which is still 0.21 during flight—but a decreased pressure in the aircraft cabin (approximately 752–812 hPa). The lower pressure inside the aircraft cabin reduces, therefore, the oxygen partial pressure to 158–171 hPa (Dalton’s law). These values for the partial pressure of oxygen correspond to a FiO₂ of 0.16 at standard atmosphere, as stated by the authors. ¹